The dairy industry, and more particularly the cheese industry, for many years has attempted to reduce the length of time required during the manufacturing process to obtain the desired and expected performance characteristics of a cheese. The performance characteristics most commonly associated with mozzarella cheese varieties are those exhibited when cooking these varieties on a pizza. These include melt characteristics as to the degree of blistering, meltdown, stretch, and tenderness. The capability of shortening the aging process, or eliminating it altogether, has significant economic benefits directly associated with the costs of aging cheese.
Mozzarella variety cheeses are made by a process involving the following steps:
a) pasteurizing cow's milk having a fat content in the range of about 1.5 to 3.5 weight percent (in some countries water buffalo milk is used);
b) fermenting the milk with one or more lactic acid-producing bacteria to obtain a cheese milk;
c) coagulating the cheese milk to obtain a coagulum comprised of curd and whey;
d) cutting the coagulum and draining the whey therefrom, thereby leaving a cheese curd;
e) heating, kneading, and stretching the cheese curd until it is a homogeneous, fibrous mass having a moisture content in the range of about 45 to 60 weight percent and a milkfat content of at least about 30 weight percent (dried solids basis);
f) placing the mass in a bath of cold brine and leaving it there long enough to achieve cooling and salt penetration: and
g) removing the cooled cheese from the brine.
After the brining step the resultant unripened mozzarella cheese traditionally has been aged at about 35.degree. to 45.degree. F. for approximately seven to 21 days, to develop characteristic taste and texture, as well as acceptable baking characteristics. (The aging process also is sometimes referred to as "ripening," "curing," or "maturation.") All of the major components of cheese, i.e., carbohydrates, protein, and fat, are subject to change during aging. Through a complex variety of metabolic processes, e.g., enzymatic lipolysis and proteolysis, these principal components are metabolized to lactic acid, peptides, amino acids, and fatty acids.
After aging, the mozzarella cheese often is comminuted and frozen, so as to halt the ripening processes, and then shipped in refrigerated containers. It may be frozen in block form as well, but seldom, if ever, is.
The baking characteristics of mozzarella cheese are very important. Most mozzarella cheese is used to make pizzas. This entails spreading tomato sauce and the cheese (in comminuted form) on a base of pizza crust and then baking the resultant pizza in an oven maintained at a temperature in the range of about 400.degree. to 1000.degree. F., often within the range of about 450.degree. to 650.degree. or 850.degree. F. As is well known, a great variety of other food materials, such as pepperoni slices, mushroom slices, ground beef, sausage, and pineapple chunks, may be used as toppings on the pizza as well. As the cheese melts, the cheese components begin to fluidize, which can result in water evaporation, release of oil, and blistering. What is desirable is that the cheese thoroughly melt before the crust is overbaked. What is undesirable is that the cheese form many large blisters as it melts. The blisters, which are formed by the protein, can burn, creating dark hard scabs that can detract from the appearance, taste, and mouth feel of the pizza. To be satisfactory, the cheese needs to melt with minimal blistering, while the crust bakes.
If not subjected to an aging step, mozzarella variety cheeses have tended to blister significantly when used to make baked pizzas. The higher the oven temperature, the greater the risk of blistering.
Ripening of mozzarella variety cheeses requires considerable time, space, and energy, however, which adds to the cost of the finished product. The same is true of other varieties of cheese as well, to a greater or lesser extent. For this reason many approaches have been tried in an attempt to find ways to accelerate the ripening process for several types of cheese.
Lederer, in 1953, disclosed that the aging time for American cheddar cheese can be shortened by quick freezing the cheese when green, holding it frozen for 60 to 180 minutes, and then transferring the cheese to a conventional aging room maintained at 45.degree. to 60.degree. F. Good body, texture, and flavor is achieved after only nine days of aging, as contrasted with at least six weeks by the conventional process. (Lederer, U.S. Pat. No. 2,816,036, "Cheese Manufacture," filed May 1, 1953, issued Dec. 10, 1957.)
Freeman, in 1959, disclosed that the aging of cheddar cheese can be accelerated by using a mixture of cultures and a higher temperature (60.degree. F.) for the first four weeks. (Freeman, "Accelerating the Aging Process in Cheddar Cheese," Kentucky Agric. Experiment Station, U. Kentucky, Bulletin 666 (June 1959).)
Kristofferson, in 1967, taught that the addition of reduced glutathione and porcine lipase to a slurry of the cheese will accelerate the ripening of cheddar when making a cheese paste. (Kristofferson, et al. "Cheddar Cheese Flavor. IV. Directed and Accelerated Ripening Process," J. Dairy Sci. Vol. 50, No. 3, 292-297 (1967).)
Singh, in 1969, disclosed that the aging of cheddar cheese curd while in slurry form can be accelerated by the addition of sodium citrate and a combination of vitamins and minerals. (Singh, et al., "Factors Affecting Flavor Development in Cheddar Cheese Slurries," J. of Dairy Sci. Vol. 53, No. 5, 533-536 (1969).)
Prochazka, in 1971, disclosed the addition of sodium citrate to "mozzarella-type" cheeses to shorten the ripening period by at least one-third. (Czechoslovak Patent No. 141,283, "Process for the Production of Cheeses with Accelerated Ripening," May 15, 1971.)
Sullivan et al., in 1973, disclosed that American cheese and Swiss cheese can be ripened two to five times faster by adding adenosine-3',5'-cyclic monophosphate to the cheese curd. (Sullivan et al., U.S. Pat. No. 3,859,446, "Method for Rapid Curing of Cheese," filed Sep. 26, 1973, issued Jan. 7, 1975.)
Sutherland, in 1975, taught that the time required to ripen cheddar cheese slurries can be shortened by adjusting a variety of different conditions, including headspace oxygen in the aging vessel. (Sutherland, "Rapidly Ripening Cheese Curd Slurries in Processed Cheese Manufacture," the Australian J. of Dairy Tech., Vol. 30, 138-142 (1975).)
Shehata et al., in 1977, taught that the addition of sodium citrate to raw water buffalo milk accelerates lipolysis and proteolysis of Ras cheese prepared therefrom (Shehata et al., "Effect of Adding Sodium Citrate to Buffaloes' Milk on Chemical and Organoleptic Properties of Ras Cheese," Dairy Sci. Abstracts, Vol. 41, No. 9, 550 (1979).)
Lee, in 1979, proposed injecting a pregastric esterase solution into mozzarella cheese to shorten the aging process. (Lee, Hyong Joo, "Acceleration of Cheese Ripening High Pressure Injection and Diffusion of Curing Components in Italian-Type Cheese," Ph.D. Thesis, U. Wisconsin-Madison, 1979.) Lee's thesis includes a literature review on the acceleration of cheese ripening. Id., 2-45. He reports that the ripening process, like most chemical reactions, is accelerated at higher temperatures, but in many cases undesirable reactions also occur, yielding off-flavored products. Id., at 17.
Abdel Baky, in 1982, reported the results of experiments demonstrating that the addition of sodium citrate, proteinase, and lipase to a Ras cheese slurry can shorten the curing time from two months to seven days. (Abdel Baky, et al., "Ripening Changes in Cephalotyre `Ras` Cheese Slurries," J. Dairy Research, Vol. 49, 337-341 (1982).)
Law, in 1987, wrote that the ripening of various cheeses can be accelerated by the addition of exogenous proteolytic enzymes. (Law, Barry A., "Proteolysis in Relation to Normal and Accelerated Cheese Ripening," Cheese: Chemistry, Physics and Microbiology (Elsevier Applied Science, New York, N.Y. 1987, Edited by P. F. Fox, vol. 1, ch. 10, 365-392.) (Adding lipases or esterases has been common practice in Italian-type cheese manufacture since the 1950's.)
With regard to all of these prior art processes, however, some amount of aging has been indicated as being necessary.